Dedicated listening room design

Thanks for all your input -- most helpful as usual. I've decided to use Dietrich RC Deluxe resilient channels on the walls and ceilings, double 5/8" drywall w/ Green Glue between the sheets on the walls and double 1/2" drywall & Green Glue on the ceiling, wall-to-wall carpeting, and LED lights (contractor says they're the quietest w/ dimmer) if budget permits. R30 insulation or maybe special insulation, again if budget permits. Not sure about absorbers/diffusors yet, but I'll fight that battle another day after the room's done.

Thanks again, and I'll follow up with results after it's done in case anybody's interested.

Soix - I was in your shoes about 5 years ago. Exciting times and certainly enought to learn that will take some time to digest and internalize.

Using my basement 2-channel room as an example, here are some of my learnings:
* use a solid core exterior door to keep sound inside the room
* HVAC: I used a round flexible tube with sound insulation on the inside. You want to install it in such a way that there are several near-90 degree bends in it to prevent sound from traveling back to the furnace and up through the rest of the house. Also, baseboard heaters are dead quiet as another option.
* Lighting: don't use dimmers! They hum and your stereo system will pick it up. Instead use lights that work on 120volts (assuming you're in North America) and that don't use a transformer which can introduce humm.
* use J-molding and an acoustic sealant between the ceiling and walls so that if the walls move they don't transfer energy to the ceiling and vice versa.
* your wall-to-wall carpet will absorb much high end energy so you will need to pay attention to how you treat your room's surfaces so as not to create a dead sounding room with low reverb time for middle and high frequencies. Try using reflection (i.e. bare wall) and diffusion for middle and upper frequencies and absorption for bass frequencies.
* get a Dayton Audio Omnimic or XTZ or similar product to take in room measurements so you can do before and after measurements to gauge how effective your treatments are.
* buy Toole's book.
* not all reflections are created equally. Address reflections from the back and front wall as they are the least beneficial.
* experiment with reflection vs absorption vs diffusion at the side wall's 1st reflection points. Reflection provides the widest apparent sound source and maintains the mid/high freq energy whereas absorption narrows the sound source and attenuates the mid/high freq energy but usually allows for the best retrival of musical details. Diffusion is like the best of both - it widens the apparent sound source to something more akin to a live performance while preserving the mid/high freq energy and allows nearly as much musical detail retrival as absorption. Personal taste prevails.
* If you're considering diffusion within your room and if the sitting distance to the side and rear walls is short, then use diffusion that either is two dimensional (e.g. RPG Skylines) so that only about 50% of the sound is scattered back to you latterally, or a diffuser that doesn't provide temporal effects (e.g. phase) such as geometrical shapes like round surfaces.

Pictures in my 'System' will show what I speak of.

And have fun as it's an itterative trial and error kind of experience.

Kevinzoe,
I have absorption on the side walls. I also have wall to wall carpeting, and think i may be overdamped. Would you recommend trying a pair of the GIK d1's at the 1st reflection points?

I use absorption on the side walls and it's not overdamped. As long as you leave space between the treatments you should be ok.

One man's overdamped...

Personally, I've been in several highly-damped rooms and don't like them. For me they suck the life out of the listening experience, although I agree you can focus on the individual sounds since you don't have to be bothered with all those pesky ambient cues.

Anyway, after reading the Geddes book it was most helpful to learn that some reflections can be good (taste-dependent of course) and can enhance the listening experience if, like me, you like to hear those things. That's why I'm going with bare walls and was planning on diffusers on the side walls and absorptive stuff behind the equipment -- not sure what yet.

Problem - I really want dimmers and recessed lighting. I'm running dedicated lines and my builder is recommending LED lights, so I'm hoping that will somewhat mitigate the effects of a dimmer if I can find a good one. No? Do LED lights come in 120V, and are those the ones to get? Too many options sometimes.

I'm concerned about getting the junction between the ceiling and walls right since my builder isn't well-versed in these things and it could really screw up the works (I'm also concerned about his workers short-circuiting the hell out of my resilient channels as well).

This is exciting, but it's also more than a little frightening since a lot of these decisions can't be easily (or cheaply) reversed. Ugh.